1. Field
Embodiments of the invention relate to radio frequency identification (RFID) components and methods. In particular, embodiments of the invention relate to RFID reader system components and methods.
2. Background Information
Radio frequency identification (RFID) systems typically include RFID tags and RFID readers. RFID readers are also known as RFID reader/writers or RFID interrogators. RFID systems may be used in many ways for locating and identifying objects to which the tags are attached. RFID systems are particularly useful in product-related and service-related industries for tracking large numbers of objects being processed, inventoried, or handled. In such cases, an RFID tag is usually attached to an individual item, or to its package.
In principle, RFID techniques entail using an RFID reader to interrogate one or more RFID tags. The reader transmitting a Radio Frequency (RF) wave performs the interrogation. A tag that senses the interrogating RF wave responds by transmitting back another RF wave. The tag generates the transmitted back RF wave either originally, or by reflecting back a portion of the interrogating RF wave in a process known as backscatter. Backscatter may take place in a number of ways.
The reflected-back RF wave may further encode data stored internally in the tag, such as a number. The response is demodulated and decoded by the reader, which thereby identifies, counts, or otherwise interacts with the associated item. The decoded data may denote a serial number, a price, a date, a destination, other attribute(s), any combination of attributes, and so on.
An RFID tag typically includes an antenna system, a radio section, a power management section, and frequently a logical section, a memory, or both. In earlier RFID tags, the power management section included an energy storage device, such as a battery. RFID tags with an energy storage device are known as active tags. Advances in semiconductor technology have miniaturized the electronics so much that an RFID tag may be powered solely by the RF signal it receives. Such RFID tags do not include an energy storage device, and are called passive tags.
FIG. 1 is a block diagram of components of a typical RFID system 100. An RFID reader system 101 transmits an interrogating radio frequency (RF) wave 102. RFID tag 104 in the vicinity of RFID reader system 101 may sense interrogating RF wave 102, and generate RF wave 103 in response. RFID reader system 101 senses and interprets wave 103.
Reader system 101 and tag 104 exchange data via wave 102 and wave 103. In a session of such an exchange, each encodes, modulates, and transmits data to the other, and each receives, demodulates, and decodes data from the other. The data is modulated onto, and decoded from, RF waveforms.
Encoding the data in waveforms may be performed in a number of different ways. For example, protocols are devised to communicate in terms of symbols, also called RFID symbols. A symbol for communicating may be a delimiter, a calibration symbol, and so on. Further symbols may be implemented for ultimately exchanging binary data, such as “0” and “1”, if that is desired. In turn, when the waveforms are processed internally by reader system 101 and tag 104, they may be equivalently considered and treated as numbers having corresponding values, and so on.
Tag 104 may be a passive tag or an active tag, i.e. having its own power source. Where tag 104 is a passive tag, it is powered from wave 102.
FIG. 2A is a block diagram showing a detail of a prior art RFID reader system 201, which may be the same as RFID reader system 101 shown in FIG. 1. RFID reader system 201 includes an RFID reader device 206, which is also known as a reader box, or just box. The box has at least one port 207-1. As shown, in some embodiments it has four ports 207-1, 207-2, 207-3, and 207-4. Each port may have an antenna driver. For each port there is an output, which is typically a coaxial cable plug. Accordingly cables 208-1, 208-2, 208-3, and 208-4 may be attached to the outputs of the provided respective ports 207-1, 207-2, 207-3, and 207-4, and then the cables 208-1, 208-2, 208-3, and 208-4 may each be attached to one of four respective antennas 209-1, 209-2, 209-3, and 209-4.
Each port may send to its respective antenna a driving signal that is in the RF range. The driving signal causes the antenna to transmit an RF wave, which is analogous to RF wave 102 of FIG. 1. In addition, the RF wave may be backscattered from RFID tags, analogous to RF wave 103 of FIG. 1. The backscattered RF wave then ultimately becomes a signal sensed by the port.
The RFID reader device also has other components, such as hardware and software, which are described in more detail later in this document. The components control the ports, and as such cause RF wave to be sent, and the sensed backscattered RF wave to be interpreted. Optionally and preferably there is a communication link to other equipment, such as a server 205 or the like, for remote operation of system 201.
One drawback to the prior art RFID reader system of FIG. 2A is that the number of antennas is limited by the number of ports on the RFID reader device. In some cases it is desirable to add or otherwise use more antennas than are available on an existing or given RFID reader device. One option is to acquire a different RFID reader device with more ports. Another option is to procure additional RFID reader devices. However, buying an additional RFID reader device or box tends to add additional cost. Additionally, one place in which RFID reader systems are commonly employed is around dock doors in warehouses. Multiple RFID reader devices may tend to complicate assembly or configuration, for example around the dock door.
FIG. 2B is a block diagram showing a detail of another prior art RFID reader system 201, which may be the same as RFID reader system 101 shown in FIG. 1. RFID reader system 201 has a few components similar to those of FIG. 2A. The differences are now described.
A multiplexer 228 is coupled to first port 207-1 of RFID reader box 206. A first antenna 209-1 and a second antenna 209-2 are each coupled with an output of multiplexer 228. An RF signal may be provided from the RFID reader device to the multiplexer.
The multiplexer may switch between providing the RF signal to the first antenna or the second antenna. The multiplexer may receive a signal from the RFID reader system that controls whether the multiplexer switches to the first antenna or the second antenna.